Engineered annexin A5 variants have impaired cell entry for molecular imaging of apoptosis using pretargeting strategies

Recombinant protein diannexin prevents preeclampsia-like symptoms in a pregnant mouse model via reducing the release of microparticles

Preeclampsia (PE) is characterized by placenta-mediated pregnancy complication. The only effective treatment for PE is the delivery of the placenta. However, this treatment may cause preterm birth and neonatal death. Therefore, preventing PE is needed. The mechanism of PE involves abnormal placentation, which leads to the release of anti-angiogenic and inflammatory mediators into maternal circulation. These mediators contribute to systemic vascular dysfunction, inflammatory responses, and excessive thrombin generation. Microparticles (MPs) are reportedly involved in PE by promoting the thromboinflammatory response. This study describes a strategy to prevent PE by reducing MP release using the recombinant protein, diannexin. Results showed that the patients with PE had elevated MP number and procoagulant activity and increased NLRP3 inflammasome activation. Additionally, diannexin remarkably reduced the release of MPs from activated cells by binding to phosphatidylserine exposed on the surface of activated cells. Moreover, in vivo results showed that diannexin could prevent PE-like symptoms by decreasing MPs and NLRP3 inflammasome activation in pregnant mice. Furthermore, diannexin effectively inhibited trophoblast cell activation and NLRP3 inflammasome activation in vitro. These findings suggested that diannexin inhibited MP release and might be an effective therapeutic strategy for preventing PE.

Rational design of a ratiometric two-photon fluorescent probe for real-time visualization of apoptosis

A dialdehyde-functionalized ratiometric two-photon fluorescent probe (Mito-DCHO) based on a symmetric carbazole-containing two-dimensional ICT system was rationally designed for cysteine-specific detection in mitochondria, which was utilized for real-time assessing and dual-channel visualization of the early stage of apoptosis by monitoring mitochondrial oxidative stress levels.

Phenoxide-Bridged Zinc(II)-Bis(dipicolylamine) Probes for Molecular Imaging of Cell Death

Cell death is involved in many pathological conditions, and there is a need for clinical and preclinical imaging agents that can target and report cell death. One of the best known biomarkers of cell death is exposure of the anionic phospholipid phosphatidylserine (PS) on the surface of dead and dying cells. Synthetic zinc(II)-bis(dipicolylamine) (Zn2BDPA) coordination complexes are known to selectively recognize PS-rich membranes and act as cell death molecular imaging agents. However, there is a need to improve in vivo imaging performance by selectively increasing target affinity and decreasing off-target accumulation. This present study compared the cell death targeting ability of two new deep-red fluorescent probes containing phenoxide-bridged Zn2BDPA complexes. One probe was a bivalent version of the other and associated more strongly with PS-rich liposome membranes. However, the bivalent probe exhibited self-quenching on the membrane surface, so the monovalent version produced brighter micrographs of dead and dying cells in cell culture and also better fluorescence imaging contrast in two living animal models of cell death (rat implanted tumor with necrotic core and mouse thymus atrophy). An (111)In-labeled radiotracer version of the monovalent probe also exhibited selective cell death targeting ability in the mouse thymus atrophy model, with relatively high amounts detected in dead and dying tissue and low off-target accumulation in nonclearance organs. The in vivo biodistribution profile is the most favorable yet reported for a Zn2BDPA complex; thus, the monovalent phenoxide-bridged Zn2BDPA scaffold is a promising candidate for further development as a cell death imaging agent in living subjects.

Pharmacological Treatment with Annexin A1 Reduces Atherosclerotic Plaque Burden in LDLR-/- Mice on Western Type Diet

Objective

To investigate therapeutic effects of annexin A1 (anxA1) on atherogenesis in LDLR^-/- mice.

Methods

Human recombinant annexin A1 (hr-anxA1) was produced by a prokaryotic expression system, purified and analysed on phosphatidylserine (PS) binding and formyl peptide receptor (FPR) activation. Biodistribution of ^99mTechnetium-hr-anxA1 was determined in C57Bl/6J mice. 12 Weeks old LDLR^-/- mice were fed a Western Type Diet (WTD) during 6 weeks (Group I) or 12 weeks (Group P). Mice received hr-anxA1 (1 mg/kg) or vehicle by intraperitoneal injection 3 times per week for a period of 6 weeks starting at start of WTD (Group I) or 6 weeks after start of WTD (Group P). Total aortic plaque burden and phenotype were analyzed using immunohistochemistry.

Results

Hr-anxA1 bound PS in Ca²⁺-dependent manner and activated FPR2/ALX. It inhibited rolling and adherence of neutrophils but not monocytes on activated endothelial cells. Half lives of circulating ^99mTc-hr-anxA1 were <10 minutes and approximately 6 hours for intravenously (IV) and intraperitoneally (IP) administered hr-anxA1, respectively. Pharmacological treatment with hr-anxA1 had no significant effect on initiation of plaque formation (-33%; P = 0.21)(Group I) but significantly attenuated progression of existing plaques of aortic arch and subclavian artery (plaque size -50%, P = 0.005; necrotic core size -76% P = 0.015, hr-anxA1 vs vehicle) (Group P).

Conclusion

Hr-anxA1 may offer pharmacological means to treat chronic atherogenesis by reducing FPR-2 dependent neutrophil rolling and adhesion to activated endothelial cells and by reducing total plaque inflammation.

Quantitative analysis of annexin V-membrane interaction by flow cytometry

We constructed a green fluorescent phosphatidylserine (PS)-binding probe, which was generated by fusing enhanced green fluorescent protein (EGFP) to the C terminus of human annexin V (anxV). With this probe, we investigated anxV-membrane interaction under different calcium and anxV-EGFP concentrations through flow cytometry (FCM). A mathematical description of the binding characteristics is proposed and validated to quantify the relationship concerning the relative concentration of membrane-bound anxV (B), calcium concentration ([C]), and protein concentration ([P]). Further analyses reveal that [Formula: see text] is linear with [Formula: see text] or [Formula: see text] when [P] and [C] are fixed, respectively, which indicates that the anxV-membrane binding reaction may involve sequential multiple steps. Our study provides a reference for application of anxV in apoptosis detection. The mathematical expression facilitates exploration of the possible interactions between calcium, anxV, and membrane. The corresponding mathematical analysis strengthens the interpretation of the interaction data.

Molecular imaging of cell death in tumors. Increasing annexin A5 size reduces contribution of phosphatidylserine-targeting function to tumor uptake

OBJECTIVE

Annexin A5 is a phosphatidylserine binding protein that binds dying cells in vivo. Annexin A5 is a potential molecular imaging agent to determine efficacy of anti-cancer therapy in patients. Its rapid clearance from circulation limits tumor uptake and, hence, its sensitivity. The aim of this study is to determine if non-invasive imaging of cell death in tumors will benefit from increasing circulation time of annexin A5 by increasing its size.

PROCEDURES

Annexin A5 size was increased by complexation of biotinylated annexin A5 with Alexa-Fluor680-labeled streptavidin. The non-binding variant of annexin A5, M1234, was used as negative control. The HT29 colon carcinoma xenograft model in NMRI nude mice was used to measure tumor uptake in vivo. Tumor uptake of fluorescent annexin A5-variants was measured using non-invasive optical imaging.

RESULTS

The annexin A5-streptavidin complex (4 ∶ 1, moles:moles, Mw ∼ 200 kDa) binds phosphatidylserine-expressing membranes with a Hill-coefficient of 5.7 ± 0.5 for Ca2+-binding and an EC50 of 0.9 ± 0.1 mM Ca2+ (EC50 is the Ca2+ concentration required for half maximal binding)(annexin A5: Hill-coefficient 3.9 ± 0.2, EC50 1.5 ± 0.2 mM Ca2+). Circulation half-life of annexin A5-streptavidin is ± 21 minutes (circulation half-life of annexin A5 is ± 4 min.). Tumor uptake of annexin A5-streptavidin was higher and persisted longer than annexin A5-uptake but depended less on phosphatidylserine binding.

CONCLUSION

Increasing annexin A5 size prolongs circulation times and increases tumor uptake, but decreases contribution of PS-targeting to tumor uptake and abolishes power to report efficacy of therapy.

Topical delivery of Avastin to the posterior segment of the eye in vivo using annexin A5-associated liposomes

Effective delivery to the retina is presently one of the most challenging areas in drug development in ophthalmology, due to anatomical barriers preventing entry of therapeutic substances. Intraocular injection is presently the only route of administration for large protein therapeutics, including the anti-Vascular Endothelial Growth Factors Lucentis (ranibizumab) and Avastin (bevacizumab). Anti-VEGFs have revolutionised the management of age-related macular degeneration and have increasing indications for use as sight-saving therapies in diabetes and retinal vascular disease. Considerable resources have been allocated to develop non-invasive ocular drug delivery systems. It has been suggested that the anionic phospholipid binding protein annexin A5, may have a role in drug delivery. In the present study we demonstrate, using a combination of in vitro and in vivo assays, that the presence of annexin A5 can significantly enhance uptake and transcytosis of liposomal drug carrier systems across corneal epithelial barriers. This system is employed to deliver physiologically significant concentrations of Avastin to the posterior of the rat eye (127 ng/g) and rabbit retina (18 ng/g) after topical application. Our observations provide evidence to suggest annexin A5 mediated endocytosis can enhance the delivery of associated lipidic drug delivery vehicles across biological barriers, which may have therapeutic implications.

Annexin a5 as a new potential biomarker for Cisplatin-induced toxicity in human kidney epithelial cells

Cisplatin is a member of platinum-containing anti-cancer drugs that causes cross-linking of DNA and ultimately cancer cell apoptosis. The therapeutic function of cisplatin on various types of cancers has been widely reported but the side effects have been discovered together and nephrotoxicity has been regarded as major side effect of cisplatin. To select candidates for new sensitive nephrotoxicity biomarker, we performed proteomic analysis using 2-DE/MALDI-TOF-MS followed by cisplatin treatment in human kidney cell line, HK-2 cells, and compared the results to the gene profi le from microarray composed of genes changed in expression by cisplatin from formerly reported article. Annexin A5 has been selected to be the most potential candidate and it has been identifi ed using Western blot, RT-PCR and cell viability assay whether annexin A5 is available to be a sensitive nephrotoxic biomarker. Treatment with cisplatin on HK-2 cells caused the increase of annexin A5 expression in protein and mRNA levels. Overexpression of annexin A5 blocked HK-2 cell proliferation, indicating correlation between annexin A5 and renal cell toxicity. Taken together, these results suggest the possibility of annexin A5 as a new biomarker for cisplatin-mediated nephrotoxicity.

Gallium-68: chemistry and radiolabeled peptides exploring different oncogenic pathways

Abstract Early and specific tumor detection and also therapy selection and response evaluation are some challenges of personalized medicine. This calls for high sensitive and specific molecular imaging such as positron emission tomography (PET). The use of peptides for PET molecular imaging has undeniable advantages: possibility of targeting through peptide-receptor interaction, small size and low-molecular weight conferring good penetration in the tissue or at cellular level, low toxicity, no antigenicity, and possibility of wide choice for radiolabeling. Among β(+)-emitter radioelements, Gallium-68 is a very attractive positron-emitter compared with carbon-11 or fluorine-18 taking into account its easy production via a (68)Ge/(68)Ga generator and well established radiochemistry. Gallium-68 chemistry is based on well-defined coordination complexes with macrocycle or chelates having strong binding properties, particularly suitable for linking peptides that allow resistance to in vivo transchelation of the metal ion. Understanding specific and nonspecific molecular mechanisms involved in oncogenesis is one major key to develop new molecular imaging tools. The present review focuses on peptide signaling involved in different oncogenic pathways. This peptide signalization might be common for tumoral and non-tumoral processes or could be specific of an oncological process. This review describes gallium chemistry and different (68)Ga-radiolabeled peptides already in use or under development aiming at developing molecular PET imaging of different oncological processes.

Longitudinal bioluminescence imaging of the dynamics of Doxorubicin induced apoptosis

Objectives: Most chemotherapy agents cause tumor cell death primarily by the induction of apoptosis. The ability to noninvasively image apoptosis in vivo could dramatically benefit pre-clinical and clinical evaluation of chemotherapeutics targeting the apoptotic pathway. This study aims to visualize the dynamics of apoptotic process with temporal bioluminescence imaging (BLI) using an apoptosis specific bioluminescence reporter gene. Methods: Both UM-SCC-22B human head and neck squamous carcinoma cells and 4T1 murine breast cancer cells were genetically modified with a caspase-3 specific cyclic firefly luciferase reporter gene (pcFluc-DEVD). Apoptosis induced by different concentrations of doxorubicin in the transfected cells was evaluated by both annexin V staining and BLI. Longitudinal BLI was performed in xenografted tumor models at different time points after doxorubicin or Doxil treatment, to evaluate apoptosis. After imaging, DNA fragmentation in apoptotic cells was assessed in frozen tumor sections using TUNEL staining. Results: Dose- and time-dependent apoptosis induced by doxorubicin in pcFluc-DEVD transfected UM-SCC-22B and 4T1 cells was visualized and quantified by BLI. Caspase-3 activation was confirmed by both caspase activity assay and Glo^TM luciferase assay. One dose of doxorubicin treatment induced a dramatic increase in BLI intensity as early as 24 h after treatment in 22B-pcFluc-DEVD xenografted tumors. Sustained signal increase was observed for the first 3 days and the fluorescent signal from ex vivo TUNEL staining was consistent with BLI imaging results. Long-term imaging revealed that BLI signal consistently increased and reached a maximum at around day 12 after the treatment with one dose of Doxil. Conclusions: BLI of apoptosis with pcFluc-DEVD as a reporter gene facilitates the determination of kinetics of the apoptotic process in a real-time manner, which provides a unique tool for drug development and therapy response monitoring.

Biomarkers and molecular probes for cell death imaging and targeted therapeutics

Cell death is a critically important biological process. Disruption of homeostasis, either by excessive or deficient cell death, is a hallmark of many pathological conditions. Recent research advances have greatly increased our molecular understanding of cell death and its role in a range of diseases and therapeutic treatments. Central to these ongoing research and clinical efforts is the need for imaging technologies that can locate and identify cell death in a wide array of in vitro and in vivo biomedical samples with varied spatiotemporal requirements. This review article summarizes community efforts over the past five years to identify useful biomarkers for dead and dying cells, and to develop molecular probes that target these biomarkers for optical, radionuclear, or magnetic resonance imaging. Apoptosis biomarkers are classified as either intracellular (caspase enzymes, mitochondrial membrane potential, cytosolic proteins) or extracellular (plasma membrane phospholipids, membrane potential, surface exposed histones). Necrosis, autophagy, and senescence biomarkers are described, as well as unexplored cell death biomarkers. The article discusses possible chemotherapeutic and theranostic strategies, and concludes with a summary of current challenges and expected eventual rewards of clinical cell death imaging.

Cell surface-expressed phosphatidylserine as therapeutic target to enhance phagocytosis of apoptotic cells

Impaired efferocytosis has been shown to be associated with, and even to contribute to progression of, chronic inflammatory diseases such as atherosclerosis. Enhancing efferocytosis has been proposed as strategy to treat diseases involving inflammation. Here we present the strategy to increase 'eat me' signals on the surface of apoptotic cells by targeting cell surface-expressed phosphatidylserine (PS) with a variant of annexin A5 (Arg-Gly-Asp-annexin A5, RGD-anxA5) that has gained the function to interact with α(v)β(3) receptors of the phagocyte. We describe design and characterization of RGD-anxA5 and show that introduction of RGD transforms anxA5 from an inhibitor into a stimulator of efferocytosis. RGD-anxA5 enhances engulfment of apoptotic cells by phorbol-12-myristate-13-acetate-stimulated THP-1 (human acute monocytic leukemia cell line) cells in vitro and resident peritoneal mouse macrophages in vivo. In addition, RGD-anxA5 augments secretion of interleukin-10 during efferocytosis in vivo, thereby possibly adding to an anti-inflammatory environment. We conclude that targeting cell surface-expressed PS is an attractive strategy for treatment of inflammatory diseases and that the rationally designed RGD-anxA5 is a promising therapeutic agent.

Protective effect of the apoptosis-sensing nanoparticle AnxCLIO-Cy5.5

The diagnostic utility of the apoptosis-sensing nanoparticle (NP), AnxCLIO-Cy5.5, is well established. Here we sought to define the pathophysiological impact of the nanoparticle (NP) on apoptotic cells. Confocal microscopy showed that AnxCLIO-Cy5.5 remained bound to apoptotic cell membranes for 3 hours but by 7 hours had become completely internalized. AnxCLIO-Cy5.5 exposure did not impact energetics, metabolism or caspase-3 activity in apoptotic cells. Gene expression in cells exposed to AnxCLIO-Cy5.5 did not reveal upregulation of pro-inflammatory or cell-death pathways. Moreover, exposure to AnxCLIO-Cy5.5 decreased the frequency of membrane rupture of early apoptotic cells. Similarly, in mice exposed to 1 hour of ischemia -reperfusion, the injection of AnxCLIO-Cy5.5 at the onset of reperfusion reduced infarct size/area at risk by 16.2%. Our findings suggest that AnxCLIO-Cy5.5 may protect apoptotic cells by stabilizing their cell membranes and has the potential to become a theranostic agent, capable of both identifying and salvaging early apoptotic cells. From the Clinical Editor: This study demonstrates that AnxCLIO-Cy5.5 nanoparticles may protect apoptotic cells by cell membrane stabilization and have the potential to become a "theranostic agent" capable of identifying and salvaging early apoptotic cells.